Electrical system for aircraft

ABSTRACT

Systems and methods associated with electrical systems of aircraft are disclosed. A method disclosed herein comprises generating electricity using an electric generator operatively coupled to an engine of the aircraft, supplying the electricity generated using the electric generator to a baseline power bus; generating electricity using an electric starter generator operatively coupled to the engine; and supplying the electricity generated using the electric starter generator to a supplemental power bus independent from the baseline power bus.

CROSS-REFERENCE TO RELATED APPLICATION AND CLAIM OF PRIORITY

The present application claims priority to U.S. Provisional PatentApplication Ser. No. 62/681,323 filed on Jun. 6, 2018, the entirecontents of which are hereby incorporated by reference.

TECHNICAL FIELD

The disclosure relates generally to aircraft, and more particularly toelectrical systems of aircraft.

BACKGROUND

Specialized “special mission” aircraft can carry specialized equipmentfor special (e.g. sometimes unique) mission requirements. Suchspecialized equipment can comprise electric loads additional to thebasic electric loads of the aircraft. Accordingly, specialized aircraftcan require specialized electrical systems that are configured toaccommodate the needs of such specialized equipment. Since, aspecialized electrical system can have an architecture that issignificantly different from a baseline electrical system of a similarbut non-specialized aircraft that is already certified, sucharchitecture of the specialized electrical system must be separatelycertified by the applicable certification authorities.

SUMMARY

In one aspect, the disclosure describes an electrical system for aspecialized aircraft. The system comprises:

-   -   an electric generator operatively coupled to an engine of the        aircraft;    -   a baseline power bus configured to distribute electricity to one        or more baseline electric loads, the electric generator        supplying electricity to the baseline power bus when the        electric generator is driven by the engine;    -   an electric starter generator operatively coupled to the engine,        the electric starter generator being configured to operate as a        motor to start the engine and to operate as a generator when        driven by the engine; and    -   a supplemental power bus configured to distribute electricity to        one or more supplemental electric loads different from the one        or more baseline electric loads, the supplemental power bus        being independent from the baseline power bus, the electric        starter generator supplying electricity to the supplemental        power bus when the electric starter generator is driven by the        engine.

The electric generator and the electric starter generator may beoperatively coupled to the engine via separate mounting pads on a sameaccessory gearbox.

The electric starter generator may be operatively coupled to the enginevia an adaptor gearbox.

The electric generator and the electric starter generator may be housedin a nacelle of the engine.

The supplemental power bus may be connectable to a battery for poweringthe electric starter generator during starting of the engine.

The supplemental power bus may be connectable to an electric generatoroperatively coupled to an auxiliary power unit.

The supplemental power bus may be connectable to a power source externalto the aircraft.

In some embodiments of the electrical system, the engine is a firstengine, the electric generator is a first electric generator, thebaseline power bus is a first baseline power bus, the one or morebaseline electric loads are one or more first baseline electric loads,the electric starter generator is a first electric starter generator,the supplemental power bus is a first supplemental power bus and the oneor more supplemental electric loads are one or more first supplementalelectric loads, the system comprises:

-   -   a second electric generator operatively coupled to a second        engine of the aircraft;    -   a second baseline power bus configured to distribute electricity        to one or more second baseline electric loads, the second        electric generator supplying electricity to the second baseline        power bus when the second electric generator is driven by the        second engine;    -   a second electric starter generator operatively coupled to the        second engine, the second electric starter generator being        configured to operate as a motor to start the second engine and        to operate as a generator when driven by the second engine; and    -   a second supplemental power bus configured to distribute        electricity to one or more second supplemental electric loads        different from the one or more second baseline electric loads,        the second supplemental power bus being independent from the        second baseline power bus, the second electric starter generator        supplying electricity to the second supplemental power bus when        the second electric starter generator is driven by the second        engine.

The first and second supplemental busses may be configured to permitpower transfer between the first and second supplemental busses.

The first electric starter generator may be connectable to receiveelectricity from the second electric starter generator during startingof the first engine.

Embodiments can include combinations of the above features.

In another aspect, the disclosure describes a method of operating anelectrical system of a specialized aircraft. The method comprises:

-   -   generating electricity using an electric generator operatively        coupled to an engine of the aircraft;    -   supplying the electricity generated using the electric generator        to a baseline power bus;    -   generating electricity using an electric starter generator        operatively coupled to the engine; and    -   supplying the electricity generated using the electric starter        generator to a supplemental power bus independent from the        baseline power bus.

The method may comprise transferring motive power from the engine to theelectric generator and to the electric starter generator via a sameaccessory gearbox.

The method may comprise transferring motive power from the engine to theelectric starter generator via a an adaptor gearbox.

The method may comprise connecting the supplemental power bus to abattery for powering the electric starter generator during starting ofthe engine.

The method may comprise connecting the supplemental power bus to anelectric generator operatively coupled to an auxiliary power unit forpowering the electric starter generator during starting of the engine.

The method may comprise connecting the supplemental power bus to anelectric generator operatively coupled to a power source external to theaircraft for powering the electric starter generator during starting ofthe engine.

In some embodiments of the method, the electric starter generator is afirst electric starter generator and the engine is a first engine, themethod comprises supplying electricity to the first electric startergenerator from a second electric starter generator operatively coupledto a second engine during starting of the first engine.

The electric generator and the electric starter generator may be housedin a nacelle of the engine.

Embodiments can include combinations of the above features.

In a further aspect, the disclosure describes a method for increasing anelectric generating capacity of an aircraft comprising an engine, anair-powered starter for starting the engine and an electric generatorconfigured to be driven by the engine and supply electricity to a firstpower bus. The method comprises:

-   -   uncoupling the air-powered starter from the engine;    -   operatively coupling an electric starter generator to the engine        for starting the engine;    -   adding a second power bus to the aircraft, the second power bus        being independent from the first power bus; and    -   configuring the electric starter generator to be driven by the        engine and supply electricity to the second power bus.

The method may comprise:

-   -   uncoupling the air-powered starter from a mounting pad of an        accessory gearbox operatively coupled to the engine; and    -   operatively coupling the electric starter generator to the        engine via the mounting pad.

The electric generator may be operatively coupled to the engine via anaccessory gearbox and the method may comprise operatively coupling theelectric starter generator to the engine via the accessory gearbox.

The method may comprise coupling the electric starter generator to theengine via an adaptor gearbox.

The method may comprise housing the electric starter generator in anacelle of the engine.

The second power bus may be connectable to a battery for powering theelectric starter generator during starting of the engine.

The second power bus may be connectable to a power source external tothe aircraft for powering the electric starter generator during startingof the engine.

The second power bus may be connectable to an electric generatoroperatively coupled to an auxiliary power unit for powering the electricstarter generator during starting of the engine.

The method may comprise modifying a nacelle of the engine to accommodatethe electric starter generator.

Embodiments can include combinations of the above features.

In a further aspect, the disclosure describes an aircraft comprising asystem as disclosed herein.

Further details of these and other aspects of the subject matter of thisapplication will be apparent from the detailed description includedbelow and the drawings.

DESCRIPTION OF THE DRAWINGS

Reference is now made to the accompanying drawings, in which:

FIG. 1 is a top plan view of an exemplary aircraft comprising aspecialized system;

FIG. 2A is a schematic representation of an exemplary baseline system ofthe aircraft of FIG. 1;

FIG. 2B is a schematic representation of an exemplary specialized systemof the aircraft of FIG. 1;

FIG. 3 is a flowchart illustrating a method for operating thespecialized system of the aircraft of FIG. 2B;

FIG. 4 is a flowchart illustrating a method for increasing the electricgenerating capacity of an aircraft;

FIG. 5A is a schematic representation showing an accessory gearbox ofthe aircraft of FIG. 1 with an air-powered starter coupled to theaccessory gearbox;

FIG. 5B a schematic representation showing the accessory gearbox of FIG.5A with the air-powered starter is uncoupled from the accessory gearbox;and

FIG. 5C a schematic representation showing the accessory gearbox of FIG.5A with an electric starter generator coupled to the accessory gearbox.

DETAILED DESCRIPTION

The following disclosure relates to specialized (e.g., “specialmission”) aircraft that are equipped to meet special missionrequirements. Specialized aircraft can sometimes be produced byconverting an existing and certified baseline aircraft configuration tomeet the special mission requirements. Specialized aircraft (e.g.,search and rescue, maritime patrol, communications management, commandand control, troop and/or cargo transport, aerial survey, meteorologicalmeasurements, medical evacuation, air ambulance, air hospital, flightinspection) can have non-conventional specialized mission-specificequipment (e.g., radars, jammers, medical equipment, communicationsequipment, self-protection systems, etc.) that is not normally onboard apassenger aircraft designed for civil aviation for example. Accordingly,the specialized equipment can comprise supplemental electric loadsadditional to baseline aircraft electric loads and can requiresupplemental electric generating capacity that is beyond thealready-certified baseline electrical system architecture of thebaseline aircraft that is being converted.

In various embodiments, the methods and systems disclosed herein canfacilitate the conversion of an already-certified baseline aircraft intoa specialized aircraft. For example, the systems and methods disclosedherein can facilitate the increase of electric generating capacity of anaircraft without significantly altering the existing baseline electricalsystem architecture of the aircraft. In some embodiments, a methoddisclosed herein can comprise replacing an air-powered starter coupledto an engine of the aircraft with an electric starter generator wherethe electric starter generator powers a supplemental power bus that isindependent from one or more baseline power busses of the aircraft. Theuse of an electric starter generator instead of air-powered starter canincrease the electricity generating capacity onboard an aircraft that isbeing converted to a specialized aircraft. In some situations, the useof an electric starter generator instead of an air-powered starter canalso improve control over the starting of the engine and also providereliability and/or maintenance improvements. In some embodiments, theuse of an electric starter generator in combination with a supplementalpower bus that is independent from one or more baseline power busses ofthe aircraft being converted allows for some or all of the baselinealready-certified electrical system architecture to be retained on thespecialized aircraft in order to reduce certification efforts for thespecialized aircraft.

Aspects of various embodiments are described through reference to thedrawings.

FIG. 1 is a top plan view of an exemplary aircraft 10, which cancomprise specialized electrical system 12B as described below. Aircraft10 can be any type of aircraft such as corporate (e.g., business jet),private, commercial and passenger aircraft suitable for civil aviation,that has been converted into a specialized aircraft. For example,aircraft 10 can be a narrow-body, twin-engine jet airliner or can be anultra-long range business jet. Aircraft 10 can be a fixed-wing aircraft.Aircraft 10 can comprise wings 14, fuselage 16, one or more engines 18and empennage 20.

FIG. 2A is a schematic representation of an exemplary baselineelectrical system 12A of a baseline (i.e., non-specialized) version ofaircraft 10. Baseline system 12A can correspond to an already-certifiedsystem architecture that is configured to accommodate the basic electricneeds of the baseline version of aircraft 10 that is being convertedinto a specialized aircraft. Even though FIG. 2A illustrates a baselinesystem 12A that comprises two engines 18A, 18B, it is understood thataspects of this disclosure are also applicable to aircraft that includea single engine 18A or that include two or more engines 18A, 18B.

In the exemplary embodiment illustrated, baseline system 12A cancomprise electric generators 22A, 22B (referred generally herein usingreference numeral 22) operatively coupled to respective engines 18A, 18B(referred generally herein using reference numeral 18) via respectiveaccessory gearboxes (AGBs) 24A, 24B (referred generally herein usingreference numeral 24). Each electric generator 22 can be configured tosupply electricity to a respective baseline power bus 26A or 26B(referred generally herein using reference numeral 26) when driven bythe respective engine 18. Each baseline power bus 26 can be configuredto distribute electricity to one or more baseline electric loads 28A,28B (referred generally herein using reference numeral 28). Baselineelectric loads 28 can comprise electric loads that serve the basic needsof aircraft 10 and that can be included in the baseline configuration ofaircraft 10. Each baseline power bus 26 can be connectable to respectiveone or more baseline electric loads 28 via one or more contactors 30.

In some embodiments of baseline system 12A, two or more electricgenerators 22A can be operatively coupled to engine 18A via AGB 24A andsuch two or more electric generators 22A can be configured to supplyelectricity to one or more baseline power busses 26A. Similarly, in someembodiments, two or more electric generators 22B can be operativelycoupled to engine 18B via AGB 24B and such two or more electricgenerators 22B can be configured to supply electricity to one or morebaseline power busses 26B.

AGBs 24 can each comprise one or more mounting pads 32 for interfacingwith suitable accessories such as electric generators, starters andpumps during operation of engines 18. For example, one or more mountingpads 32 can be used to extract motive power from engines 18 for drivingelectric generators 22 and/or hydraulic pumps 34A, 34B via respectiveAGBs 24. One or more mounting pads 32 can be used to inject motive powerinto engines 18 via respective air-powered (e.g., turbine) starters(ATS's) 36A, 36B (referred generally herein using reference numeral 36).Air-powered starters 36 can be used during starting of respectiveengines 18. Air-powered starters 36 can be powered with compressed airproduced by an auxiliary power unit (APU) 38 which can be onboardaircraft 10 or with compressed air supplied by a ground-basedsource/cart external to aircraft 10. Compressed air generated by APU 38can be delivered to air-powered starters 36 via suitable ducts 40 andvalves 42.

APU 38 can comprise a device that supplies energy (e.g., electricity,compressed air) for functions other than propulsion. In someembodiments, APU 38 can comprise a gas turbine engine. Electricgenerator 22C can be operatively coupled to be driven by APU 38.Electric generator 22C can be configured to supply electricity tobaseline power bus 26C. Baseline power bus 26C can be configured todistribute electricity to one or more baseline loads 28C. Direct current(DC) starter 44 can be operatively coupled to APU 38 for the purpose ofstarting APU 38. DC starter 44 can be powered by electricity provided bybattery 46 via contactor 30.

FIG. 2B is a schematic representation of an exemplary specializedelectrical system 12B of specialized aircraft 10. In some embodiments,specialized system 12B can be a modification of baseline system 12Ashown in FIG. 2A. Elements of specialized system 12B already describedabove in relation to baseline system 12A are referenced using likereference numerals. Even though FIG. 2B illustrates a specialized system12B that comprises two engines 18A, 18B, it is understood that aspectsof this disclosure are also applicable to aircraft that include a singleengine 18A or that include more than two engines 18A, 18B. For example,in some embodiments, system 12B can include electric generator 22A,baseline power bus 26A, electric starter generator 48A and supplementalpower bus 50A. Baseline power bus 26A can be configured to distributeelectricity to one or more baseline electric loads 28A. Electricgenerator 22A can be operatively coupled to engine 18A so as to bedriven via motive power extracted from engine 18A via AGB 24A forexample. Electric generator 22A can supply electricity to baseline powerbus 26A when electric generator 22A is driven by engine 18A. Electricstarter generator 48A can be operatively coupled to engine 18A. Electricstarter generator 48A can be configured to operate as a motor to startengine 18A and to operate as a generator when driven by engine 18A.Supplemental power bus 50A can be configured to distribute electricityto one or more supplemental electric loads 52A that are different fromthe one or more baseline electric loads 28A. Electric starter generator48A can supply electricity to supplemental power bus 50A when electricstarter generator 48A is driven by motive power extracted from engine18A via AGB 24A for example.

Electric starter generator 48A can be of any suitable type that providesrequired electrical power when operating as a generator and thatprovides required torque when operating as a motor. In variousembodiments, electric starter generator 48A can provide DC voltage(e.g., 270 V) or variable frequency AC voltage (e.g., 115/230 V or230/400 V). In some embodiments, electric starter generator 48 can be avariable frequency starter generator. In some embodiments, electricstarter 48 can be a DC brushless starter generator

In some embodiments of specialized system 12B, two or more electricgenerators 22A can be operatively coupled to engine 18A via AGB 24A andsuch two or more electric generators 22A can be configured to supplyelectricity to one or more baseline power busses 26A. Similarly, in someembodiments, two or more electric generators 22B can be operativelycoupled to engine 18B via AGB 24B and such two or more electricgenerators 22B can be configured to supply electricity to one or morebaseline power busses 26B.

In some embodiments, supplemental power bus 50A can be independent(i.e., segregated) from baseline power bus 26A. Power busses 26A, 50Acan each comprise a common wire/conductor to which one or more powerusers (i.e., electric loads) are connected. For example, each power bus26A, 50A can be a common source of power for one or more relatedelectrical loads 28A or 52A. Power busses 26A and 50A can be part ofrespective independent electrical sub-systems. For example, baselinepower bus 26A can be part of a baseline (e.g., previously certified)electrical system that is configured to cater to the baseline needs ofaircraft 10, and, supplemental power bus 50A can be part of supplementalelectrical system that is configured to cater to the specializedequipment of specialized aircraft 10.

Power busses 26A and 50A can be independent from each other in that theycan have their own separate power sources and their own separateelectric loads. For example, the electricity supplied to baseline powerbus 26A can be generated independently of the electricity supplied tosupplemental power bus 50A via separate electric generator 22A andelectric starter generator 48A respectively. In some embodiments,baseline power bus 26A and supplemental power bus 50A can be (e.g.,permanently) electrically isolated from each other so that no exchangeof electricity is possible between the two power busses 26A, 50A.Accordingly, in some embodiments, there are no interconnections betweenthe two power busses 26A, 50A. In some embodiments where no exchange ofelectricity is possible between power busses 26A, 50A, baseline powerbus 26A and supplemental power bus 50A can be non-redundant. Theindependence (i.e., segregation) of baseline power bus 26A andsupplemental power bus 50A and their associated electrical systemsallows for some or all of the already-certified baseline electricalsystem architecture to be retained in specialized aircraft 10 and canconsequently simplify certification efforts for specialized aircraft 10.

In some embodiments, electric generator 22A and electric startergenerator 48A can be operatively coupled to engine 18A via separatemounting pads 32 on the same AGB 24A. In cases where the implementationof specialized system 12B includes the replacement of air-poweredstarter 36A with electric starter generator 48A, the same (i.e.,starter) mounting pad 32 from which air-powered starter 36A is removedcan be used to operatively couple electric starter generator to AGB 24A.

Specialized system 12B can comprise power converter and controller 54configured to selectively control one or more contactors 30 ofspecialized system 12B and consequently control the flow/distribution ofelectricity throughout part of specialized system 12B. Power converterand controller 54 can also include suitable power converting and/orconditioning equipment. The actions of power converter and controller 54can be based on one or more inputs such as sensed inputs, pilotcommands, commands from other operators or other systems of aircraft 10that may be in communication with power converter and controller 54.Power converter and controller 54 can comprise one or more dataprocessors and one or more computer-readable memories storingmachine-readable instructions executable by the data processor(s) andconfigured to cause power converter and controller 54 to perform stepsto implement a computer-implemented process. In some embodiments, powerconverter and controller 54 can be configured to carry out powerdistribution functions by controlling the state of one or morecontactors 30. For example, supplemental power bus 50A can beselectively connectable to battery 46 for powering electric startergenerator 48A during starting of engine 18A. For example, powerconverter and controller 54 can be configured to, in response to anengine start command, establish an electrical connection between startergenerator 48A and battery 46 (or other power source(s)) by controllingthe state of one or more contactors 30. In some embodiments, powerconverter and controller 54 can be configured to provide suitable DC toDC power conversion of electricity supplied to electric startergenerator 48A from battery 46 during starting of engine 18A for example.

In the context of a multi-engine aircraft, system 12B can furtherinclude electric generator 22B, baseline power bus 26B, electric startergenerator 48B and supplemental power bus 50B. Baseline power bus 26B canbe configured to distribute electricity to one or more baseline electricloads 28B. Electric generator 22B can be operatively coupled to engine18B so as to be driven via motive power extracted from engine 18B viaAGB 24B for example. Electric generator 22B can supply electricity tobaseline power bus 26B when electric generator 22B is driven by engine18B. Electric starter generator 48B can be operatively coupled to engine18B. Electric starter generator 48B can be configured to operate as amotor to start engine 18B and to operate as a generator when driven byengine 18B. Supplemental power bus 50B can be configured to distributeelectricity to one or more supplemental electric loads 52B that aredifferent from the one or more baseline electric loads 28B. Electricstarter generator 48B can supply electricity to supplemental power bus50B when electric starter generator 48B is driven by motive powerextracted from engine 18B via AGB 24B for example. It is understood thatthe description provided above in relation to electric generator 22A,baseline power bus 26A, electric starter generator 48A and supplementalpower bus 50A is also applicable to electrical systems that rely onmultiple engines for power generation.

Even though, FIG. 2B illustrates the use of both engines 18 for thegeneration of supplemental electric power, it is understood that,depending on the needs, specialized system 12B can make use of fewerthan all engines available on aircraft 10 for the generation ofsupplemental electric power (e.g., using electric starter generator 48)for powering supplemental electric loads 52.

In various embodiments, supplemental power busses 50A, 50B (referredgenerally herein using reference numeral 50) may or may not beindependent from each other. For example, in some embodiments anexchange of electricity between supplemental power busses 50A, 50B canbe possible via the actuation of one or more contactors 30 under thecontrol of power converter and controller 54 or otherwise. Accordingly,in some embodiments, supplemental power busses 50A, 50B can be at leastpartially redundant. For example, in some embodiments, specializedsystem 12B can be configured to permit either or both electric startergenerators 48A, 48B (referred generally herein using reference numeral48) to supply electricity to either or both of supplemental busses 50A,50B. In some embodiments, specialized system 12B can be configured topermit either or both electric starter generators 48A, 48B to supplyelectricity to baseline electric bus 26C for example. In someembodiments, specialized system 12B can be configured to permit eitheror both electric starter generators 48A, 48B to receive electricity frombattery 46 (e.g., via power converter and controller 54) during startingof engines 18A, 18B for example.

In some embodiments, specialized system 12B can be configured to permiteither or both supplemental power busses 50A, 50B to receive electricityfrom external power source 55, which can be external to aircraft 10 andconnectable to specialized system 12B when aircraft 10 is on the groundfor example. Such external power source 55 can be used to power one ormore supplemental loads 52A, 52B when engines 18A, 18B are off forexample. Such external power source 55 can be used to power electricstarter generator 48 (e.g., via power converter and controller 54)during starting of engine 18 for example. Such external power source 55can be used to power DC starter 44 during starting of APU 38 and/or topower baseline electric load(s) 28C via power converter and controller54.

In some embodiments, specialized system 12B can be configured toselectively permit either or both electric starter generators 48A, 48Bto receive electricity from electric generator 22C (e.g., via powerconverter and controller 54) during starting of engines 18A, 18B forexample.

In some embodiments, specialized system 12B can be configured toselectively permit electric starter generators 48A to receiveelectricity from electric generator 48B (e.g., via power converter andcontroller 54) during starting of engine 18A for example.

In some embodiments, specialized system 12B can be configured toselectively permit electric starter generators 48B to receiveelectricity from electric generator 48A (e.g., via power converter andcontroller 54) during starting of engine 18B for example.

In some embodiments where engine 18A is disposed on a first (e.g., lefthand side) of aircraft 10 and engine 18B is disposed on a second (e.g.,right hand side) of aircraft 10, baseline load(s) 28A and supplementalload(s) 52A can be disposed on the first side of aircraft 10, and,baseline load(s) 28B and supplemental load(s) 52B can be disposed on thesecond side of aircraft 10.

FIG. 3 is a flowchart illustrating method 100 for operating thespecialized system 12B of specialized aircraft 10. Method 100 can beperformed using specialized system 12B as shown in FIG. 2B or othersystem architectures. Method 100 can comprise:

-   -   generating electricity using electric generator 22 operatively        coupled to engine 18 of aircraft 10 (see block 102);    -   supplying the electricity generated using electric generator 22        to baseline power bus 26 (see block 104);    -   generating electricity using electric starter generator 48        operatively coupled to engine 18 (see block 106); and    -   supplying the electricity generated using electric starter        generator 48 to supplemental power bus 50 independent from        baseline power bus 26 (see block 108).

Method 100 can comprise transferring motive power from engine 18 toelectric generator 22 and to electric starter generator 48 via a sameAGB 24. In some embodiments, method 100 can comprise transferring motivepower from engine 18 to electric starter generator 48 via adaptorgearbox 56 (shown in FIG. 5C).

In some embodiments, method 100 can comprise connecting supplementalpower bus 50 to battery 46 for powering electric starter generator 48during starting of engine 18.

In some embodiments, method 100 can comprise connecting supplementalpower bus 50 to electric generator 22C operatively coupled to APU 38 forpowering electric starter generator 48 during starting of engine 18.

In some embodiments, method 100 can comprise connecting supplementalpower bus 50 to power source 55 external to aircraft 10 for poweringelectric starter generator 48 during starting of engine 18.

In some embodiments, method 100 can comprise supplying electricity toelectric starter generator 48A from electric starter generator 48Boperatively coupled to engine 18B (while engine 18B is operating) duringstarting of engine 18A.

FIG. 4 is a flowchart illustrating method 200 for increasing an electricgenerating capacity of an aircraft comprising engine 18, air-poweredstarter 36 for starting engine 18 and electric generator 22 configuredto be driven by engine 18 and supply electricity to baseline power bus26. The description of method 200 below is made in reference to FIGS. 2Aand 2B and also in reference to FIGS. 5A-5C. In some embodiments, method200 can facilitate the conversion of a baseline aircraft to aspecialized aircraft 10. Method 200 can comprise:

-   -   uncoupling air-powered starter 36 from engine 18 (see block        202);    -   operatively coupling electric starter generator 48 to engine 18        for starting engine 18 (see block 204);    -   adding supplemental power bus 50 to aircraft 10, supplemental        power bus 50 being independent from baseline power bus 26; and    -   configuring electric starter generator 48 to be driven by engine        18 and supply electricity to supplemental power bus 50 (see        block 206).

In some embodiments, method 200 can comprise replacing air-poweredstarter 36 with electric starter generator 48 on a same mounting pad 32of AGB 24 operatively coupled to engine 18. In other words, method 200can comprise uncoupling air-powered starter 36 from mounting pad 32 ofAGB 24 and operatively coupling electric starter generator 48 to engine18 via the same mounting pad 32. Uncoupling air-powered starter 36 cancomprise physically removing air-powered starter 36 from engine 18.

In some embodiments, method 200 can comprise modifying nacelle 58 ofengine 18 to accommodate and cover electric starter generator 48.Modifying nacelle 58 can comprising expanding an amount of spaceavailable inside nacelle 58 to accommodate electric starter generator48. In some embodiments, expanding the amount of space inside nacelle 58can comprise incorporating an aerodynamically-shaped bulge in nacelle 58where the interior of such bulge can be used to accommodate electricstarter generator 48 and/or any additional equipment associatedtherewith.

In some embodiments, electric generator 22 can be operatively coupled toengine 18 via AGB 24 and method 200 can comprise operatively couplingelectric starter generator 48 to engine 18 via AGB 24. In someembodiments, method 200 can comprise coupling electric starter generator48 to engine 18 via adaptor gearbox 56 (see FIG. 5C). In someembodiments, electric starter generator 48 can be housed in nacelle 58of engine 18 (see FIGS. 5A-5C).

In some embodiments, supplemental power bus 50 can be connectable tobattery 46 for powering electric starter generator 48 during starting ofengine 18.

In some embodiments, supplemental power bus 50 can be connectable topower source 55 external to aircraft 10 for powering electric startergenerator 48 during starting of engine 18.

In some embodiments, supplemental power bus 50 can be connectable toelectric generator 22C operatively coupled to APU 38 for poweringelectric starter generator 48 during starting of engine 18.

FIGS. 5A-5C schematically show a sequence of operations associated withincreasing the electric generation capacity of aircraft 10. FIG. 5A is aschematic representation of AGB 24 of engine 18 with electric generator22 and air-powered starter 36 operatively coupled to AGB 24 via separatemounting pads 32. FIG. 5A schematically shows a portion of nacelle 58which houses engine 18 and provides an aerodynamically-shaped coveringfor engine 18. AGB 24, air-powered starter 36 and electric generator 22can be housed inside nacelle 58. AGB 24 can be drivingly coupled to ashaft of engine 18 via tower shaft 60. The configuration shown in FIG.5A can be associated with baseline system 12A of FIG. 2A.

FIG. 5B a schematic representation of AGB 24 with air-powered starter 36uncoupled therefrom so as to free the associated mounting pad 32.

FIG. 5C a schematic representation of AGB 24 with electric startergenerator 48 coupled to AGB 24 via the same mounting pad 32 from whichair-powered starter 36 was uncoupled. The configuration shown in FIG. 5Ccan be associated with specialized system 12B of FIG. 2B. In someembodiments, the installation of electric starter generator 48 caninvolve the use of one or more additional brackets 62 or othersupport(s) for physically supporting electric starter generator 48. Itis understood that other peripheral (e.g., cooling) equipment (notshown) may be required for the integration of electric starter generator48 with engine 18. In some embodiments, the same or a modified nacelle58 shaped for aerodynamic efficiency can be used for housing electricstarter generator 48. In some embodiments, the same nacelle 58 can bemodified to accommodate electric starter generator 48 and associatedequipment.

In some embodiments where a change in speed ratio is required between ashaft of electric starter generator 48 and an input/output of mountingpad 32 of AGB 24, electric starter generator 48 can be operativelycoupled to AGB 24 via optional adaptor gearbox 56. Adaptor gearbox 56can be disposed between electric starter generator 48 and the applicablemounting pad 32.

The above description is meant to be exemplary only, and one skilled inthe relevant arts will recognize that changes may be made to theembodiments described without departing from the scope of the inventiondisclosed. The present disclosure may be embodied in other specificforms without departing from the subject matter of the claims. Thepresent disclosure is intended to cover and embrace all suitable changesin technology. Modifications which fall within the scope of the presentinvention will be apparent to those skilled in the art, in light of areview of this disclosure, and such modifications are intended to fallwithin the appended claims. Also, the scope of the claims should not belimited by the preferred embodiments set forth in the examples, butshould be given the broadest interpretation consistent with thedescription as a whole.

What is claimed is:
 1. An electrical system for a specialized aircraftconverted from a baseline version of the aircraft, the systemcomprising: a first electric generator operatively coupled to an engineof the aircraft; a baseline power bus configured to accommodateelectrical needs of the baseline version of the aircraft and distributeelectricity to one or more baseline electric loads, the first electricgenerator supplying electricity to the baseline power bus when the firstelectric generator is driven by the engine; an electric startergenerator operatively coupled to the engine, the electric startergenerator being configured to operate as a motor to start the engine andto operate as a generator when driven by the engine; and a supplementalpower bus configured to distribute electricity to one or moresupplemental electric loads different from the one or more baselineelectric loads, the supplemental power bus being independent from thebaseline power bus, the supplemental power bus providing generatingcapacity that is increased with respect to the baseline power bus of thebaseline version of the aircraft being converted, the electric startergenerator supplying electricity to the supplemental power bus when theelectric starter generator is driven by the engine, wherein thesupplemental power bus is connectable to a battery for powering theelectric starter generator during starting of the engine, said batteryfurther providing electricity for a direct current starter operativelyconnected to an auxiliary power unit of the specialized aircraft, saidauxiliary power unit driving a second electric generator; and whereinthe electric starter generator is operatively coupled to the engine viaan accessory gearbox and an adaptor gearbox causing a change in speedratio between a shaft of the electric starter generator and aninput/output of a mounting pad of the accessory gearbox.
 2. Theelectrical system as defined in claim 1, wherein the first electricgenerator and the electric starter generator are operatively coupled tothe engine via separate mounting pads on the accessory gearbox.
 3. Theelectrical system as defined in claim 1, wherein the first electricgenerator and the electric starter generator are housed in a nacelle ofthe engine.
 4. The electrical system as defined in claim 1, wherein thesupplemental power bus is connectable to the second electric generator.5. The electrical system as defined in claim 1, wherein the supplementalpower bus is connectable to a power source external to the aircraft. 6.The electrical system as defined in claim 1, wherein the engine is afirst engine, the baseline power bus is a first baseline power bus, theone or more baseline electric loads are one or more first baselineelectric loads, the electric starter generator is a first electricstarter generator, the supplemental power bus is a first supplementalpower bus and the one or more supplemental electric loads are one ormore first supplemental electric loads, the system comprising: a thirdelectric generator operatively coupled to a second engine of theaircraft; a second baseline power bus configured to distributeelectricity to one or more second baseline electric loads, the thirdelectric generator supplying electricity to the second baseline powerbus when the third electric generator is driven by the second engine; asecond electric starter generator operatively coupled to the secondengine, the second electric starter generator being configured tooperate as a motor to start the second engine and to operate as agenerator when driven by the second engine; and a second supplementalpower bus configured to distribute electricity to one or more secondsupplemental electric loads different from the one or more secondbaseline electric loads, the second supplemental power bus beingindependent from the second baseline power bus, the second electricstarter generator supplying electricity to the second supplemental powerbus when the second electric starter generator is driven by the secondengine.
 7. The electrical system as defined in claim 6, wherein thefirst and second supplemental busses are configured to permit powertransfer between the first and second supplemental busses.
 8. Theelectrical system as defined in claim 6, wherein the first electricstarter generator is connectable to receive electricity from the secondelectric starter generator during starting of the first engine.
 9. Anaircraft comprising the electrical system as defined in claim
 1. 10. Amethod of operating an electrical system of a specialized aircraft, themethod comprising: generating electricity using a first electricgenerator operatively coupled to an engine of the aircraft; supplyingthe electricity generated using the first electric generator to abaseline power bus configured to accommodate electrical needs of abaseline version of the aircraft; generating electricity using anelectric starter generator operatively coupled to the engine; supplyingthe electricity generated using the electric starter generator to asupplemental power bus independent from the baseline power bus, thesupplemental power bus providing generating capacity that is increasedwith respect to the baseline power bus of the baseline version of theaircraft being converted; connecting the supplemental power bus to abattery for powering the electric starter generator during starting ofthe engine, said battery further providing electricity for a directcurrent starter operatively connected to an auxiliary power unit of thespecialized aircraft, said auxiliary power unit driving a secondelectric generator; and transferring motive power from the engine to theelectric starter generator via an accessory gearbox and an adaptorgearbox causing a change in speed ratio between a shaft of the electricstarter generator and an input/output of a mounting pad of the accessorygearbox.
 11. The method as defined in claim 10, comprising transferringmotive power from the engine to the first electric generator and to theelectric starter generator via the accessory gearbox.
 12. The method asdefined in claim 10, comprising connecting the supplemental power bus tothe second electric generator for powering the electric startergenerator during starting of the engine.
 13. The method as defined inclaim 10, comprising connecting the supplemental power bus to a powerconverter and controller operatively coupled to a power source externalto the aircraft for powering the electric starter generator duringstarting of the engine.
 14. The method as defined in claim 10, whereinthe electric starter generator is a first electric starter generator andthe engine is a first engine, the method comprising supplyingelectricity to the first electric starter generator from a secondelectric starter generator operatively coupled to a second engine duringstarting of the first engine.
 15. The method as defined in claim 10,wherein the first electric generator and the electric starter generatorare housed in a nacelle of the engine.